I’ve taken several meditation workshops and been meditating for about a decade or so. There’s plenty one can get into depending on what one wants to get out of it, but as your primary focus is just on relaxation and stress relief, it’s pretty straight forward.
As others have mentioned, the most important part is getting a good comfortable position. You HAVE to be comfortable and well supported or you won’t be able to relax; however, you also don’t want to be so comfortable that you will fall asleep instead of meditate.
After you have that, really focusing on relaxing and breathing is important. For some people, it they will actually carry their thought through various parts of their body to focus on those muscles and then consciously relax them. By this I mean something like relax your toes, then your feet, then your calves…etc. It’s also important to focus on having a smooth and consistent breath.
After that, you have to relax your mind and this is probably the most difficult part for most beginners. Fortunately, there’s several ways to do it. Our minds have a way of filling in “dead air” with random thoughts, so it’s important to have a way of replacing that space with something else. As mentioned upthread, focusing on your breath can help a lot. You can also pick out a specific idea to focus on, you can count backwards, or you can even use a mantra where you pick something meaningful and think it, or even say it, over and over, to help your mind focus on that. From there, you will at times still have random thoughts, but its important just to acknowledge them and quickly put your mind back on whatever your focus is. It is helpful to minimize possible distractions by keeping the room somewhat dark and quiet, or with white noise or soft music. From there, it’s just relax, or continue to focus on whatever you’re focusing on, on something else that you want to meditate on, or simply focus on nothing.
Honestly though, some level of guidance is very helpful for starting out because I found that quieting that inner voice was definitely the most difficult part to nail down, but it shouldn’t be very difficult to find a CD or sound files online that can walk you through getting into a meditative state.
Good luck.